The effects of viruses on bodily functions is the end result of changes occuring at the cellular and subcellular levels. The pathogenic changes at the cellular level are different for different combinations of viruses and host cells. While some viruses cause a general destruction (killing) of certain cells, other may transform cells to a neoplastic state.
Important common viral infections are herpes dermatitis (including herpes labialis), herpes keratitis, herpes genitalis, herpes zoster, herpes encephalitis, infectious mononucleosis and cytomegalovirus infections all of which are caused by viruses belonging to the herpesvirus group. Other important viral diseases are influenza A and B which are caused by influenza A and B virus respectively. Another important common viral disease is viral hepatitis and especially hepatitis B virus infections are widely spread. Effective and selective antiviral agents are needed for the treatment of these diseases.
Several different viruses of both DNA and RNA type have been shown to cause tumors in animals. The effect of cancerogenic chemicals can on animals result in activation of latent tumor viruses. It is possible that tumor viruses are involved in human tumors. The most likely human cases known today are leucemias, sarcomas, breast carcinomas, Burkitt lymphomas, nasopharyngeal carcinomas and cervical cancers where RNA tumor viruses and herpes viruses are indicated. This makes the search for selective inhibitors of tumorogenic viruses and their functions an important undertaking in the effors to treat cancer.
A most important common feature of the interaction between viruses and cells is the replication or transcription of the specific viral genetic information carried by viral nucleic acids. These viral nucleic acids are of two kinds, deoxyribonucleic acids (DNA) or ribonucleic acids (RNA). The primary genetic information of the cell is carried by cell DNA. DNA and RNA synthesis involves complex enzymes called DNA and RNA polymerases respectively. The genetic information is transferred to the new nucleic acid from a template nucleic acid. There are four general ways in which these nucleic acids can be replicated or transcribed. ##STR3##
Processes 1 and 3 are used by cells. DNA viruses such as herpesviruses also use process 1 but the enzyme is different from that of the cell. RNA viruses such as influenza virus use process 2 and the RNA tumor viruses (retroviruses) can transcribe its RNA to DNA according to process 4.
The viral polymerases and the viral nucleic acid syntheses are essential not only for ordinary (productive) virus infections but also for viral transformation of cells to a neoplastic state leading to cancer (tumorogenic function of virus). In the latter case DNA produced by DNA viruses such as herpesvirus or transcribed from RNA tumor viruses and which carries the genetic information for cell transformation can be integrated into the host cell DNA. This integration, or later acts as a consequence of integration (such as interaction with cancerogenic chemicals), can then lead to the transformation of the host cell. The implications of inhibiting reverse transcriptase for cell transformation are also described in U.S. Pat. No. 3,979,511.
Since the viral polymerases in most cases differ from the cellular ones these viral enzymes and viral nucleic acid syntheses are good targets for specific antiviral chemotherapy including chemotherapy of cancer caused by viruses. It should be noted that many compounds presently used for chemotherapy of cancer are inhibitors of nucleic acid synthesis. It is therefore possible that antiviral compounds which are also inhibitors of nucleic acid synthesis can affect tumor cells directly. There is a need for an effective antiviral agent preferably having a selective inhibiting effect on a specific viral function of the virus to be combatted. It is, therefore, a general object of the present invention to provide a novel method for combatting virus infections using an antiviral agent which exerts a selective inhibiting effect on viral functions but which exerts only a negligible inhibiting effect on functions of the host cells.